An impact absorber device sometimes referred to as a “crash box” is installed on a front part of a chassis frame of a vehicle in order to absorb energy of a collision crush impact. The impact absorber device absorbs the impact energy by way of buckling deformation when a load of the impact applied thereto exceeds a predetermined level. Installation of this device thus ensures the safety of individuals in the vehicle.
In Japanese Patent Kokai No. 2002-39245, for example, such an impact absorber device made of aluminum alloy casting is disclosed.
This impact absorber device has a cylinder portion made of aluminum alloy casting, and the wall thickness of the tubular portion continuously or partially changes along an axial direction. With this configuration, the impact energy is effectively absorbed by performing plastic deformation in longitudinally alternating inward and outward corrugations along the axial direction of the tubular portion.
Japanese Patent Kokai No. 2004-100557 discloses another impact absorber device of which entire body is made of metal. This impact absorber device includes a tubular portion, flanges respectively provided on both sides of the tubular portion, and a reinforcing member formed around the tubular portion. The wall thickness of the tubular portion partially or entirely varies gradually from one side to the other.
There are other impact absorber devices which rely upon crack extension or deformation of a honeycomb element for absorbing the impact energy. An impact absorber device of crack extension type absorbs the impact energy by extending a crack which is triggered when a tapered member is pressed onto an end portion of the cylindrical element. An impact absorber device of a honeycomb element deformation type absorbs the impact energy by buckling and crashing a side wall of a honeycomb panel installed between flat plates.
Since the above mentioned conventional impact absorber devices rely on such unstable phenomena as buckling deformation and cracking extension, deformation mode (or deforming pattern) considerably changes even by slight difference in dimension, installation condition or constraint condition, which may occur during manufacturing and installation phases. Further, deformation mode is greatly influenced by the impact direction of the load at collision.
An impact absorber device of buckling type requires a longer body to absorb greater impact energy in the axial direction. This raises a concern that the longer body may cause Euler buckling during absorption of the impact energy. As a result, an absorbing element with the longer body may fail to function properly. Moreover, during the buckling deformation, the impact energy is absorbed by longitudinally alternating inward and outward corrugations as mentioned above, which generates oscillation in a load-to-length-change response. Accordingly, the entire element cannot be effectively used to absorb the impact energy.
An impact absorber device of crack extension type may vary its crack extension pattern depending on a trigger condition for the cracking such as a contact angle between the impact absorber device and a member to trigger crack in the device. Therefore, it may be very difficult to control the extension of the crack. An impact absorber device of a honeycomb element deformation type inherently has a complicated structure, and therefore it is very difficult to fabricate the device as expected and properly evaluate the performance of the device.